This invention relates to apparatus and systems for generating steam. The new system and method may allow for control of the steam generating process to output a desired steam quality from a multipath or multipass steam generator using crossover preheating of influent water flow in multiple fluid flow conduits or pipes.
Currently steam generators may be used to convert water to steam that may not be saturated. The water conversion may convert 70 percent to 80 percent of influent water to steam. The percent conversion achieved may be known as the steam quality. The unconverted or residual water may be effluent water from the steam generation process.
A single fluid flow conduit or multiple fluid flow conduits may be disposed in a heating container or vessel that may be heated by a combustible fuel, such as, a petroleum product, coal or the like. The fluid of water and steam may be heated in two steps in a steam generator convection section and in a radiant section. The steam generator may be structured for the influent water to be heated first in the convection section that may be downstream in the heated gas flow from the radiant section of the heating container. A heating gas may be at a lower temperature in the convection section relative to the radiant section. The convection section heated water may then be routed to the radiant section for heating to produce a steam effluent.
As water may be converted to steam the velocity of the fluid that may be a water and steam mixture may increase as a result of an increase in the volume of the fluid flowing in the conduit. This increase in velocity may result in an increased pressure drop in the conduit and increased conduit deterioration or wear. To reduce this effect multiple fluid flow conduit, such as, dual path or dual pass, steam generators may be used to generate steam. A dual conduit steam generator may have two approximately parallel or similar fluid flow conduits through which approximately the same total amount of water flows as may flow in a single fluid flow conduit steam generator. In a dual conduit steam generator the total water flow may be divided between the two conduits such that the fluid velocity in each conduit may be reduced which may reduce the wear on the conduits.
In a dual conduit steam generator the steam quality of the two conduit flows may be unequal as a result of differences in heat transfer rates or other factors. It may be necessary to control the water flow rate in each conduit to reduce conduit damage that may result from more water conversion to steam in one conduit relative to the other conduit. Controlling the water flow through each conduit as a function of steam quality may maintain the steam quality between each conduit as approximately equal. This method or process may result in each conduit flow producing approximately equal steam quality, but having unequal water flow.
In order to improve steam generator performance a portion of the heat energy in the water exiting the convection section may be used to heat the cooler influent water prior to its entering the convection section. Water exiting the convection section may be diverted prior to entering the radiant section and may be used to preheat the influent water. Existing steam generator systems may preheat the influent water to a temperature that may be a controlled fixed value.